Process for the production of centrifugal castings



Sept. 16, 1941. H.--PROJAIQ-INY GS I 4 PROCESS FOR THE PRODUCTION OF CENTRIFUGAL CASTIN Filed Nov. 15, 1938 fhveizbor HeUzrwh Pr ja/zm' gSept. 16, 1941 bC'dlUH UUHl PROCESS FOR THE PRODUCTION OF CENTRIFUGAL CASTINGS Heinrich Projahn, Gelsenkirchen, Germany, assignor to United States Pipe and Foundry Company, Burlington, N. J., a corporation of New Jersey Application November 15, 1938, Serial No. 240,495 In Germany November 20, 1937 (Cl. 2H5) 1 Claim.

This invention relates to the production of centrifuged castings of any desired shape, of metals of any kind, particularly for the production of centrifuged cast pipes of iron and steel.

Hitherto centrifuged cast pipes are almost exclusively produced either according to the process of de Lavaud or according to the Sandspun process. According to the former process foundry pig iron of a particular kind is cast in water cooled rotary chill moulds by means of a casting gutter which is longitudinally shiftable relatively to the mould so that the metal band depositing on the inner surface of the mould forms the pipe. Serious difl'lculties occur in this process in that the mould is very highly stressed by the hot iron coming into direct contact with it and, owing to the strong cooling effect of the mould, the pipe formed freezes in white state in its outer zone with the result that it must be Subjected to a subsequent annealing treatment.

In order to avoid the quenching effect of the mould, it has been proposed to introduce a very thin layer of lining material, in pulverous, plaitlike or plastic, band-like form into the watercooled mould before the metal is poured in. Thus, for example processes are known in which a lining layer in the form of a coherent structure deposits on the inner wall of the rotary mould, or in which a coherent feltor plait-like coating is formed on the wall of the mould by the choice of a suitable lining material, it being left to the centrifugal pressure to lay the lining material on the wall of the centrifugal mould. The centrifugal pressure exerts the same effect in the case of the known pulverous lining materials,

which are deposited on the inner wall of the mould preferably as very fine dust particles in such a thin layer that the thickness of the layer does not exceed a few hundredths of a millimetre. If it has been proposed to add a quantity of coarser particles amounting to a small fraction of the total quantity to the fine dust for the purpose of carrying the fine dust and accelerating its passage through the mould and for reducing the inflammability of the fine dust, it is nevertheless necessary for the casting of the metal taking place directly after the formation of the dust layer. The reason therefore is apparently that only during the short period which elapses before the contacting of the casting jet the dust particles are not capable of giving off the gases adhering thereto, so that the just deposited dust layer rests on a thin easily displaceable air layer which slightly reduces the off-flow of heat. This results in an improvement of the structure and the glowing period is reduced but a heat treatment is generally also necessary.

The difllculties accompanying the use of watercooled moulds are avoided by the Sandspun process. However, centrifugal casting moulds are then generally used which-as in the case of upright pipe castingare for example rammed with moist moulding sand, then placed on a centrifugal machine and cast under conditions which have to be observed for drying the moist moulding sand and uniformly distributing the metal in the mould. In order to prevent washing out of the mould lining by the inflowing casting metal hard shell-like cement layers or carbon smoothing layers are formed on the lining of the mould mass or fluxes are added to the casting metal which take up the detached particles of the lining material depositing on the inner surface of the casting. In this manner pipes are certainly obtained which are soft and require no reheating and which also can be cast from any desired kind of foundry pig iron. However, it is just the moulding sand lining which presents considerable difliculties in this process. By the ramming and drying of the sand lining and also on account of the heat effect of the casting metal the sand masses become so solidified that the pipes cannot easily be drawn, but the sand lining must be destroyed after the casting by means of complicated devices. Furthermore, the ramming of the moulds by means of a pipe model is complicated, expensive and delays the To avoid the stamping of the moulds by means of a pipe model it has also been proposed to distribute the mould mass, containing a percentage of moisture or binding agents sufficient for the caking, by centrifugal action in the rotating mould and to then prepare it by special compressing, smoothing and shaping tools such as templates or rollers, in such a manner that a sufficiently compact lining with a sufliciently smooth inner surface for the pouring in of the casting material is produced, the mass being it necessary also dried. Although an integral mould lining is formed which is itself so compact that the rotation of the lined mould can be entirely interrupted before the pouring in of the metal for the purpose of inserting the sleeve core or for transferring into the casting device proper, it is nevertheless considered necessary to impart a rotary movement to the casting metal during the feed so as to avoid its washing out effect on the mould lining. Some of the above mentioned dimcultles were also encountered in this process at the drawing of the pipes owing to the compressed mould mass.

The process according to the invention differs fundamhtally from these known processes. For carrying out the same neither mould of steel or other high-grade material accurately worked to measure, nor a foundry iron of a quite particular composition which can only be used in cooled moulds, nor an annealing of the castings produced are required. n the other hand, however, the inconvenient ramming of the moulds with sand before the casting operation or the shaping with template hitherto necessary after the moulding sand mass has been centrifuged into the mould, and the drying of the moulds before the casting operation and the tedious destruction of the sand lining after the casting are avoided by the process according to the invention. Nevertheless castings are obtained, and even castings from iron or steel, which possess the same strength properties as those produced by the de Lavaud process, but are superior thereto as regards resistance to shock.

The novel process using a lining produced by centrifugal action from sand-like materials, consists in forming in the mould or mould casing a mould lining of granular materials introduced in loose dry state in that the granular constituents of the lining are secured in their relative positions merely by applying such a high speed of rotation that a sufficiently strong and resistant adhesion of the lining is ensured to counteract the washing effect of the impinging or inflowing metal, the speed of rotation necessary to attain this being maintained during the formation of the casting.

Contrary to the general widely held opinion it has been found unexpectedly that granular materials, especially those having a considerably lower specific gravity than the casting metal, are suitable for forming an excellent supporting surface ,for the liquid centrifugal casting metal, if these materials are rotated at such a hi h p ed, accordin to the chosen thickness of the layer, their grain-size and their specific gravity, that a lining is formed having a certain permeability to gas, which lining ofiers sufficient resistance to the metal coming into contact with it, said resistance depending on the strength of the centrifugal force. Consequently, the addition of certain binding agents or a separate mechanical compressing of the materials in the mould or a working of the lining with smoothing and shaping tools, and particularly a solidifying of the mould mass by drying are not necessary, but the lining produced, according to the new process from granular materials, forms directly an ideal supporting layer possessing ample resistance for the iniiowing metal provided, at least the critical speed of rotation, determined by the physical properties of th granular materials and their layer thickness, be attained in taking into consideration the casting conditions such as diameter of centrifugal mould, specific gravity and quantity of casting material.

A particular advantage of the process according to the invention consists in that, when drawing the casting, the granular lining materials capable of trickling do not jam and that the grains can be poured out of the mould as a loose, incoherent or non-caking mass.

If metals and metal alloys which shrink strongly on solidify n such as steel and cast iron, are

,to be cast according to the new process, it is advisable to reduce the speed of rotation when the cast metal begins to solidify, so that the inner cohesion of the lining-like layer loosens, as the action of the centrifugal force decreases and enables unimpeded shrinkage of the casting in axial and radial directions.

If metal or metal alloys are cast whose structure is improved by accelerated cooling during the solidification, for example cast iron, a layer of such thickness is preferably chosen for the lining, that a cooling effect but not a quenching influence is exerted by the casting mould on the Qlidifying metal as is known in connection with dried and tightly coherent linings. The heat olfilow is thus reduced to such an extent that reheating of the casting is unnecessary even when a strongly cooled mould casing is used.

The thickness of the layer, however, depends upon the physical properties of the lining materials, especially upon its size of grain and the wall thickness of the pipes. It is preferably kept within the limits of about 1 to 20 mms., but may, if necessary to thinner or thicker according to the casting conditions.

To ensure a certain permeability to gas in the layer, the size of the grains used in preferably not smaller than 0.1 mm, By using different grain sizes it is possible to attain a roughness on the outer wall of the casting which may be desired under certain circumstances.

It may be advisable in many instances to use as lining material mixtures of granular materials of different specific gravities and of different conductivities. The latter is for example advisable when, in a part of a mould whose crosssection diiTers from that of the rest of the mould a stronger heat off-flow is to be effected without altering the thickness of the layer.

If metal and metal alloys are to be cast which have a high melting point and relatively narrow freezing interval, for example steel or cast iron, it is advisable to retard the heat off-flow not only by selecting a corresponding layer thickness for the lining but to introduce the granular lining mass into the mould in preheated or hot state.

It is not necessary to provide a special binding for the grains by a binding agent, but the centrifugal force effect, if it is only correspondingly dimensioned, is suflicient to place the components of the layer under such pressure that they can be used in absolutely dry state and under the action of the necessary speed of rotation act as a rigid, gas-permeable lining, However, a binding agent which does not generate gas under the action of the inflowing metal may be added to the granular lining mass in order, should conditions require, to enable the casting to be carried out at lower speeds of rotation than when working without binding agent. However, the size of the grain and the thickness of the layer should, in any case, be chosen so that at least the greater part of the grains are only in point contact. and a sufiicient gas permeability is ensured. Care must also be taken that the granular materials when the metal is poured in, cannot form layers which cause stoppage or filling of the gaps between the individual grains so that a shell impermeable to gas is formed. For this reason it is particularly advisable to use materials in a shape resembling as near as possible the spherical. The use of flat, elongated particles which cake together and form a coherent body is unfavourable as then there are much larger contact surfaces and the danger of fusion is in- Search R001 1.1:! r creas d, with the result that the gas permeability naturally decreases. Consequently, when flat, elongated particles are used, the influence of the layer hindering the off-flow of heat, cannot be regulated with the same certainty and reliability as when thegrains of the materials are of approximately spherical shape.

For the lining layer preferably sand-like materials come into question, such as the difierent foundry sands or oil sands; however, metals and even pulverized coal, slag and similar materials may be advantageously used provided they are in granular form and form a lining permeable to gas. It is also possible to apply on the lining thus formed and having decided granular character, or to embed in the lining materials which pass into the surface of the infiowing metal and have a refining effect on the outer skin or increase its resistance to corrosion, or which fuse on to the casting as an enamel-like coating.

To prevent the granular materials from slipping away at the portions of the mould where there are bulges or projections, such as occur in the bell-shaped portion of centrifugal cast pipes, projections, pins or the like may be fitted which prevent the slipping away. At these points, however, a sleeve-like part of bad-heat conducting material may be inserted, such as a body made of oil sand and dried-as has been proposed in a similar manner in the production of flanged pipes, but for another purpose, namely to allow the shrinkage of the pipesor a chamotte body may be inserted which preferably has the same thickness as the granular lining and behaves in a similar manner thereto as regards its action preventing the leading off of the heat.

The granular materials are preferably introduced into the mould casing in known manner by means of a tiltable gutter extending over the entire length of the casting mould and filled to the brim, so as to obtain a lining of absolutely the same thickness at all parts of the mould. The cross-sectional area of the gutter is preferably so dimensioned that, even in moulds of irregular cross-sectional shape, a pad-like lining is produced which is of the same thickness at all points, as in the case for example in tapering or stepped moulds. In such instances greater quantities of material are then fed to the mould parts of larger cross-section and accurately conform to the internal profile of the centrifugal mould under the action of the centrifugal force without it being necessary to use templates or the like. To enable only a single tiltable gutter to be used in spite of different quantities of lining material related to the longitudinal unit of the mould, inserts of different cross-section are arranged in the bottom of the tiltable gutter so that this gutter can be filled to the brim in any case in spite of the different quantities of lining material.

If tubular bodies are to be produced, it is advisable to charge the centrifugal mould lined with granular materials in known manner at a suitable inclination from the higher end preferably by means of a short run-in gutter, so that the metal, under the action of the centrifugal force deposits on the inner surface of the mould lining in the form of a spiral flowing from the interior, and thus arrives at the lower end of the rotating mould where any impurities, separating during the casting, are flushed out and can be caught by a slag pocket. In this method of production it is advantageous, according to the invention, to fit at the pouring end of the mould an insertion ring, for example of chamotte or dried oil sand or even of metal, over which ring the casting metal fiows and is spread in spiral shape towards the lower end. The procedure presents the great advantage that a pipe with absolutely smooth inner wall is produced which requires no subsequent treatment. The inclination of the mould must be such, that it is suflicient to overcome the frictional resistance of the inner surface of the lining layer, but it must not be so great that the metal shoots over the lining layer thereby forming an irregular hollow body.

This feature of my invention will perhaps be better understood by reference to the drawing forming a part of this specification in which Figure 1 is a. longitudinal central section through the upper or pouring end portion of a centrifugal mold constructed as above described, showing the run-in gutter in operative position for the pouring of the metal, the flow of the molten casting metal being indicated as it takes place at the beginning of the pouring operation and Figure 2 is a cross-section on the line 2-2 of Fig. 1, looking toward the left of said figure.

A indicates the metallic shell of the mold which, as shown, is slightly enlarged in diameter at its pouring end, as indicated at A and so as to form a shoulder as indicated at A. B indicates a refractory lining inserted in the enlarged end of the mold shell and abutted against the shoulder A, the internal diameter of this ring being such that the ring will project inwardly to a distance substantially equal to that of the loose sand lining indicated at C which is deposited in the mold while the mold is in rotation, at a speed which will cause the loose sand to distribute itself centrifugally in the form of a lining layer. D indicates the run-in gutter indicated in operative position in which it will deliver molten metal directly on to the refractory ring B. E indicates the molten metal issuing from the spout and falling on the refractory ring B of the rotating mold, in contact with which it has imparted to it a corresponding rotary movement while at the same time, by the combined influence of gravity and centrifugal force, it flows downward over the sand lining, as indicated at E while, at the same time, the centrifugal force causes it to flow upward on the refractory ring, as indicated at E. F indicates the usual form of end ring at the upper end of the mold.

It will be obvious from what I have said that the molten metal, so long as it remains in contact with the refractory ring B, which it will be understood is of a composition and character which will resist the washing effect of the metal and will have imparted to it a rotary motion approximating that of the refractory ring so that when it flows downwarc from the ring on to the sand lining it will have a rotary speed approximating that of the surface of the sand lining and, therefore, will have a greatly reduced washing effect upon the sand lining.

The following mode of operation for carrying out the process is given merely by way of example:

A cast iron centrifugal mould c sing is formed by several interconnected parts s bdivided both in axial and also in radial directions, and whose inner surface may be left in the natural state, and which, according to a modified form of the invention, may have continuous longitudinal grooves or ribs or similar unevennesses for leading off the gases, and which at the same time hold thgelining materials in known manner. This mould is slipped over a longitudinally split tube which contains the granular materials, for example silver sand necessary for the lining, and whose grain is between 0.1 to 2 mms. The centrifugal mould casing is rotated at such a speed that, the split tube being tilted, the sand is distributed uniformly over the inner surface of the mould in a layer about 3 to 5 mms. in thickness. Hereupon the mould is returned and the revolving speed increased until it attains the critical speed determined on the one hand by the physical properties of the granular lining material and by the diameter of the centrifugal mould and the thickness of the lining and on the other hand by the centrifugal pressure of the infiowing metal mass, at which speed the granular lining layer offers the necessary resistance for counteracting the action of the inflowing casting metal. A casting bucket with a short outflow gutter is now brought in front of the pouring end of the enclosed mould. The metal, on being poured into the mould rotating at constant speed, first encounters an insertion ring made for example of oil sand, chamotte or the like and is uniformly distributed thereby over the inner surface of the lining layer in spirally widening turns. When the casting metal reaches the lower end of the mould the impurities are separated as soon as the solidification has progressed sufliciently far, the speed of rotation may be reduced so that the cast body can shrink in axial and radial direction without hindrance. Cast iron of any desired composition, steel and other metals and metal alloys, and if desired other castable materials of non-metallic character may be used with equal advantage for the casting. Any kind of cast iron for example solidifies equally grey throughout.

I claim:

The process for the production of centrifugal casting, especially centrifugally cast pipes, in moulds provided with a lining of granular refractory material distributed by centrifugal efiect, consisting in introducing the lining into the mould in loose dry state, securing the granules in their relative positions by rotating the mould at such speed that said granular material offers the necessary resistance against the washing away forces of the inflowing metal, pouring the metal into said lined mould in a progressively advancing spiral stream extending throughout the length of the mould, and forming the casting while maintaining said mould at a speed sufficient for insuring the firm adhesion of the granules of the lining and the uniform distribution of the metal, the metal ein poured'initially directly onto a rigid ring of refrac orfifin'aterial'proyided arose end of theinould and having an internal diameter and rotational speed equal to that of said lining, whereby to cause the metal poured onto said ring to flow onto said granular lining with a gllcen fl aetiomumland thereby minimize the washing away effect of such metal on said granular lining.

HEINRICH PROJAH'N. 

